1. Field of the Invention
The present invention relates to devices with variable stiffness, and more specifically to such devices which have a first state which is plastically deformable or flexible or at least semi-flexible, and a second state which is less deformable or flexible than the first state. Such devices have diverse applications, e.g., for items which should be flexible for shaping, inserting, removing, opening, closing, and other physical movement, but which should be less flexible or even rigid when movement is completed and some rigidity is required. These devices may include medical devices, e.g., casts, implants, surgical devices, physiological control devices, etc.; footwear, e.g., shoes, sneakers, ski boots; headwear and sportswear, such as shoulder pads, helmet padding; furniture, e.g., seats, beds of selected firmness, shapable chairs; protective structures for goods, e.g., shaping a package to an odd shaped device; as well as other engineering and special application products.
2. Information Disclosure Statement
There have been numerous devices developed over the years which have two states, one flexible, the other rigid, and the principle of having a flexible, deformable or flowable material set in place is well known. Thus, there are plasters, amalgams, spackle, concrete, plastics, blow foams and other materials that enable a user to first shape and then set a material for custom or specialty results. However, few are capable of increased rigidity on demand, and rely-upon their own physical characteristics, e.g., drying time, polymerization or reaction time, etc. These may be slowed or sped up but cannot usually be activated on demand without the need to add a catalyst, heat, air or the like.
Further, these are even fewer devices available or known which have a formable state and a rigid state and these states are repeatable at will, e.g., the device may be cyclable back and forth between the two states. Inflatables are one exception and liquid fillable devices are another, e.g., a waterbed is readily deformable unfilled and more rigid filled. However, the inflation by water or other fluids has severe limitations due to the inherent fluid properties.
Moreover, inflation increases the device volume and the content of the pressurized medium can be inconvenient or even hazardous in some situations.
Some systems which could change its mechanical properties "on demand" can be useful in many practical applications. Since the change is due to an interaction of the material with an external impulse, they may be referred to as "interactive materials" for short.
They are a sub-class of so called "smart materials" or "smart systems" which are capable of changing their properties in general (optical, electrical, mechanical, magnetic, etc.) in response to an impulse. The "smart materials" include devices such as non-linear optical, opto-electric and piezo-electric materials. From the systems changing their mechanical properties, well-known interactive materials are the "electro-rheological fluids" which increase their viscosity (or even solidify) if placed in an external electric field. They can be used in clutches and transmissions; in hydraulic systems; in "smart structures" damping mechanical vibrations or reacting on an external stress; and are contemplated for many other uses. They have several limitations. The "solid state" is actually a rather soft gel with a relatively low yield stress. This makes them suitable only for a limited number of applications. Second, the electric field intensity required is rather high (around kV per millimeter or more). Third, some of the fluids require a certain narrow temperature range for their optimum function.
In the spite of these limitations, the systems based on the electro-rheological fluids attracted considerable interest in recent years.
Another type of known interactive system with changing properties "on demand" are so called memory materials (which are both polymers or metals). They change mechanical properties if heated over a certain temperature, and return from their "deformed" to their "inherent" shape. These systems have several inherent limitations. The change of state is triggered by reaching a certain pre-set temperature only; and the change of state (or shape) is irreversible. In spite of these limitations, these materials have numerous uses: intraocular lenses for small incision; spectacle frames; safety valves; safety switches; surgical instruments; micro-alignment devices fiber-optic splices; connectors; clamps; fasteners and many other uses.
Still another type of materials changing mechanical properties in response to the environmental changes are hydrogels. Dry, rigid "xerogels" can swell in water and change into soft, elastic hydrogels. The main limitation is the obvious dependence on the presence of water. Another limitation for some applications is the change of mass and size due to the swelling. Still another limitation is the rather lengthy and "one-way" swelling process. In spite of these limitations, hydrogels have found number of applications using this change of properties in the presence of water: seals, dilators, sensors, surgical devices insertable into body cavities (e.g., catheters) etc.
The present invention, on the other hand, relies upon an opposite mechanism, e.g., the removal of fluid to impart rigidity, and the inclusion of fluid to enhance flexibility or formability. Thus, notwithstanding the existence of flexible rigid devices, none show or suggest the present invention device using the aforesaid mechanism.